HMB Cache for SSD L2P Mapping Table
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Solution Overview
Problem
Traditional SSD architectures face challenges in efficiently managing the Flash Translation Layer (FTL) address mapping table, as DRAM-based solutions increase costs while NAND-based solutions incur high access latency.
Innovation Solution
The proposed method utilizes Host Memory Buffer (HMB) as a cache for the physical address mapping table, dividing the HMB into sections and using metadata to efficiently manage and update L2P mapping entries, thereby improving access performance and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If DRAM is used to store the L2P mapping table, then access latency is reduced, but manufacturing cost increases
Solution Approach 1:
The patent introduces HMB as an intermediary memory buffer between the host and SSD. The HMB is allocated from host system memory and used to cache frequently accessed L2P mapping entries, thereby reducing access latency without requiring expensive DRAM on the SSD side. This mediator approach allows the system to benefit from fast memory access while avoiding the cost of on-SSD DRAM.
Solution Approach 2:
The patent implements a caching strategy where only frequently accessed (hot) L2P mapping entries are stored in the HMB buffer, while less frequently accessed (cold) entries remain in NAND flash. This local quality differentiation optimizes the system by providing fast access for hot data while maintaining cost efficiency for cold data storage.
2Ease of manufacture
If HMB is used to store the L2P mapping table, then cost is reduced, but access latency increases compared to DRAM
Solution Approach 1:
The patent pre-loads frequently accessed L2P mapping entries into the HMB buffer before they are actually needed for data access operations. By anticipating which entries will be needed and loading them in advance, the system minimizes the latency penalty of using HMB instead of DRAM, as the data is already in the faster memory when needed.
Solution Approach 2:
The patent maintains continuous updates to the HMB cache as L2P mapping entries change, ensuring that the cache remains synchronized with the actual mapping table in NAND flash. This continuous maintenance of cache validity ensures that the HMB approach remains effective over time as data access patterns evolve.
3Ease of manufacture
If HMB space is limited, then cost is reduced, but the ability to store entire L2P mapping table is compromised
Solution Approach 1:
The patent divides the L2P mapping table into segments based on access frequency, with hot entries stored in HMB and cold entries stored in NAND flash. This segmentation allows the limited HMB space to be used most effectively for high-priority data while maintaining the complete mapping table across both storage media.
Solution Approach 2:
The patent implements dynamic cache management where the contents of HMB are continuously updated based on changing access patterns. As data is written or deleted from the SSD, the corresponding L2P entries are updated in both NAND flash and HMB cache, ensuring the cache adapts to current needs while working within limited space constraints.
Data Source
AI summary
This application discloses a method and system of using HMB as a cache of physical address mapping table. The method comprises: arranging physical addresses in order of logical addresses, physical mapping entries corresponding to a plurality of consecutive physical addresses form one table unit, and a logical address corresponding to a first entry of each table unit is used as an index of the table unit; determining HMB size, dividing all table units into a plurality of sections according to the HMB size, each section comprises a plurality of table units, each section is divided into a plurality of ways; calculating a metadata according to logical address corresponding to the first entry of the table unit to be stored and the HMB size, the metadata comprises a section number and a way number; writing the metadata and the table unit to be stored into the HMB. This application uses HMB as L2P address mapping table cache of SSD controller, saving or avoiding use cost of DRAM on SSD, and reducing SSD size.